Brain researchers start mapping the Human ‘Connectome’

A research effort called the Human Connectome Project is seeking to explore, define, and map the functional connections of the human brain. An update on progress in and upcoming plans for the Human Connectome Project appears in the July issue of Neurosurgery, official journal of the Congress of Neurological Surgeons. Analogous to the Human Genome Project — which mapped the human genetic code — the Human Connectome Project seeks to map “the complete, point-to-point spatial connectivity of neural pathways in the brain,” according to Arthur W. Toga, PhD, and colleagues of David Geffen School of Medicine, University of California Los Angeles. They write, “For neuroscientists and the lay public alike, the ability to assess, measure, and explore this wealth of layered information concerning how the brain is wired is a much sought after prize.” The 100 billion neurons of the human nervous system interconnect to form a relatively small number of “functional neural networks” responsible for behavior and thought. However, even after more than a century of research, there is no comprehensive map of the connections of the human brain.

Historically, studies of the human brain function have employed a “modular” view — for example, “region X is responsible for function Y.” However, a more appropriate approach is to consider which network of two or more “connected or interacting” regions is involved in a given function. Until recently, it was not possible to view networks in the living brain. But newer magnetic resonance imaging (MRI) methods sensitive to water diffusion have made it possible to create detailed maps of the underlying white matter connections between different areas of the brain. This opens the way to new approaches to mapping the structural connectivity of the brain, and showing it in ways that correspond to the brain anatomy. Researchers are working out ways to analyze these data using sophisticated modeling approaches to represent the “nodes and connections” that make up the functional networks of the brain. Such efforts are in their infancy, but these network models are capturing not only the connectedness of brain networks, but also their capacity to process information. Preliminary studies have yielded tantalizing findings, such as a link between more efficient cortical networks and increased intelligence and differences in connectedness between the right and left hemispheres of the brain. “The HCP has recently generated considerable interest because of its potential to explore connectivity and its relationship with genetics and behavior,” Dr. Toga and coauthors write.

The project has far-reaching implications for a wide range of neurological and psychiatric diseases, such as autism, schizophrenia, and Alzheimer’s disease. “The similarities and differences that mark normal diversity will help us to understand variation among people and set the stage to chart genetic influences on typical brain development and decline in human disease,” according to the authors. Dr. Toga and colleagues are making their data available for download and analysis by other researchers on the project website. In the future, the data will be openly available for exploration by the public.